This R21 research proposal, submitted in response to "Biodefense and Emerging Infectious Diseases Research Opportunities", NOT-AI-02-023, has two specific aims designed to increase our understanding of the pathogenesis of Campylobacter jejuni enterocolitis. The intestinal epithelium comprises a dynamic physical barrier that maintains an active repertoire of innate host defense responses to limit entry of clinically significant food- and water-borne pathogens. These mechanisms include the regulated production of chemokines to coordinate the appropriate innate and adaptive immune effector response. C. jejuni is a leading cause of bacterial diarrheal disease in the world. However, while relatively little is known of the pathophysiologic mechanisms employed to infect the human intestinal tract and elicit disease, interaction at the intestinal epithelium is the most common pathogenic feature of infection. The overall objective of this research proposal is to obtain novel information on the mechanisms of pathogenesis to C. jejuni enterocolitis and will, as an important first step, focus on the coordinated production of chemokines by the cells of the intestinal epithelium as a significant host defense mechanism. Studies in Aim 1 will test the hypothesis that C. jejuni infection of human intestinal epithelial cells stimulates production of chemokines for neutrophils, dendritic cells and T lymphocytes, effectors cells that we postulate act in concert to limit C. jejuni entry in vivo. A culture model intestinal epithelium will be infected with C. jejuni and the signaling mechanisms regulating epithelial chemokine production assessed. To define bacterial pathogenicity, studies in Aim 2 will utilize C. jejuni mutants to test the hypothesis that specific Campylobacter virulence factors induce host epithelial cell chemokine expression. Induction of epithelial chemokine expression will be tested in C. jejuni flagella mutants, as well as mutants selected from candidates revealed from a promoter trap-based approach to define novel virulence factors. Together, these studies will provide new insights into the cellular signaling mechanisms and bacterial gene products regulating intestinal epithelial chemokine production as a central host defense function to C. jejuni. Understanding the cellular and biochemical mechanisms of intestinal epithelial host defense to human C. jejuni infection are central to the development of preventative therapeutic strategies to modulate host-pathogen interactions to favor the host.